Exploding and colliding stars, seen as supernovae and cosmic gamma-ray
bursts, produce the brightest and most powerful radiation outbursts in
the Universe. Their observation to a distance of billions of
light-years gives us information about the accelerated expansion of
the cosmos. When a neutron star or a black hole is born during the
explosion, this releases in a very short time more energy than a star
such as our Sun produces in its whole lifetime.

Supernovae and their remnants are studied by observations at
different wavelengths of radiation (center) as well as supercomputer
simulations (left and right). The Image at the center shows
the Cassiopeia A gas nebula, the diffuse remnant of a supernova that
exploded around 1680
(green and blue: X-ray; yellow: optical;
red: infrared;
souces: NASA/CXC/SAO; NASA/STScI; NASA/JPL-Caltech/Steward/Oliver
Krause et al. (Max-Planck-Institut für Astronomie)).

On the one hand such an event can be very destructive, but on the
other hand there would not be any planets, plants or animals without
these cosmic catastrophes. These explosions drive the galactic matter
cycle, during which many generations of stars and supernovae forge the
heavy elements (heavier than helium) before these are - distributed by
the stellar explosions into the surrounding universe - being recycled
in new stars and planetary systems.

The astrophysicist Hans-Thomas Janka studies the complex, physical
processes in supernova explosions with computer models. In the next
Café & Kosmos he will talk about the fascination regarding these
events, the large challenges associated with the exact modelling of the
explosion in three dimensions, and the hopes (and fears) connected
with the next stellar explosion in our Milky Way.